In modern communication systems, a demand for high data transmission rates has resulted in the use of advanced signal standards for enhanced spectral efficiency. All-digital transmitter architectures (ADT), which employ radio-frequency (RF) power amplifiers (PA) in switched-mode operation, have shown a promising potential of achieving high power efficiency while maintaining good linearity of the transmitted signals. It is very challenging to drive switched-mode power amplifiers (SMPA) with high resolution RF input signals, and reduction of amplitude resolution of the SMPA input is needed in practice to adjust for switched-mode operation. Reduction of resolution is commonly performed through a procedure called power encoding, where a high resolution input signal is converted into a multi-level piecewise constant SMPA driving signal.
Pulse width modulation (PWM) is a technique used to reduce resolution of a PA driving signal. PWM maps a baseband input signal into a digital pulse train, where the amplitude information of the input signal is encoded into time-varying width of the pulses. In this case, an output signal of PWM includes an infinite number of modulated harmonics as noise components. Furthermore, when PWM is digitally implemented, additional in-band noise is created due to the spectral aliasing effects caused by time-sampling nature of the input and output signals. In general, these noise components are reduced by adjusting parameters used in the circuit, such as a sampling ratio of the input signal. However, such a noise reduction scheme is varied for circuit designs, and there is no consistent method to reduce the noise components of the modulated harmonics in digital signal transmission.
Thus, there is a need to provide an advanced noise shaping quantizing method and architecture for digital wireless transmission while maintaining high efficiency.